Yay! One thing to check out is whether or not the RSVP function on the website will stop people from RSVPing for more people than are invited. Our wedding website is through theknot.com and I picked it specifically because it can stop people from RSVPing for more people than we invited! But I agree that wedding websites are awesome! They are so useful for conveying info to guests.

@Beckster329: i have put a limit on it for maximum of two people per RSVP. Most people we are inviting are couples there may be the odd one who has 3 people on the invite but i will ask them to write the name of all atending guests in the comments box.

Its quite clear it sas replying on behalf of yourself, them replying on behalf of yourself and 1 other invited guest so they know hat the +1 has to actually be invited. I might write in the descripton names of invited guests appear on your invite or something to that effect. Then put something like unfortunately due to restrictions at our chosen venue, children are not permited.